The present invention relates to a bar code reader, and more particularly to a bar code reader for reading a bar code displayed on a surface of an object which is situated at a distance using a laser beam.
Recently, there is widely generalized a system in which information such as a manufacturer's name, a trade name, a price, the date of production or the like is printed as a bar code on surfaces of goods, the bar code thus printed is read by means of an optical bar code reader and thereby sale, stock or the like is managed.
There has been proposed a laser beam scanning type bar code reader. The laser beam scanning type bar code reader comprises a laser oscillator for outputting a laser beam, beam scanning means for scanning the laser beam at a constant scanning angle, detection means including a photocell for receiving light reflected by a screen of the bar code, converting the received light into an electric signal according to a quantity of the received light and outputting the electric signal, and identification means for identifying the bar code based on the electric signal.
According to the laser beam scanning type bar code reader, the laser beam is automatically scanned. Therefore, the laser beam scanning type bar code reader has an advantage that it is not required to move a scanning head with being come in contact with the object differently from a pen type bar code reader. Namely, in a fixed type bar code reader having each means incorporated in a case which can be fixed, it is sufficient to hold the object by hand. Moreover, in a hand held type bar code reader having the device incorporated in a box which can be held by hand, it is sufficient to aim at the bar code.
The length of the bar code to be read in a scanning direction depends on a standard, for example, within about 2 to 10-odd cm. To generalize the bar code reader, it is required to correspond to the bar code having the various lengths. Accordingly, a scanning angle of the laser beam scanned by the laser beam scanning means is set large such that the bar code having a length of about 10-odd cm can be read with a normal distance (for example, about 10 cm) kept between the bar code reader and the bar code screen.
On the other hand, in the bar code reader of which scanning angle is set large in order to be adapted to the long bar code, the laser beam is scanned on a plurality of bar codes at a time if the plurality of bar codes are displayed in the scanning direction. Accordingly, both the bar code to be read and the bar code not to be read are captured in a locus on the screen of the scanned laser beam, that is, a scanning area. Therefore, there is a problem that the bar code to be read cannot be identified but the bar code not to be read is inputted.
It is also considered that the distance between the bar code reader and the bar code screen is adjusted according to the length of the bar code to be read by means of the bar code reader of which scanning angle is set so as to be adapted to the bar code having an average length and thereby only the bar code to be read is captured in the scanning area. In this case, however, it is difficult for an operator to optimize the distance at every reading operation. If the distance is long, a read error is occurred because the intensity of the light reflected by the bar code screen is lowered or the aim is moved easily.